1. Field of the Invention
The present invention relates to a camera which is provided with a zoom lens and a lens capable of being mounted onto the zoom lens in a detachable manner to modify the focal length and magnifying power of the zoom lens.
2. Description of the Related Art
Conventionally available as one type of camera is the one provided with a zoom lens and a conversion lens which is mounted onto the zoom lens in a detachable manner to modify the focal length and power of the zoom lens.
Referring to drawings, the conventional arrangement of the zoom lens and the conversion lens which is mounted onto the zoom lens in a detachable manner to modify the focal length and magnification of the zoom lens is discussed below. FIG. 1 is a diagrammatic view showing the arrangement of a conventional camera comprising a zoom lens and a conversion lens which is mounted onto the zoom lens to modify the focal length and power of the zoom lens.
A zoom lens unit 100 comprises a first (front) lens group 101 mounted onto a lens casing as shown in FIG. 1.
Disposed behind the first lens group 101 is a second lens group (hereinafter referred to as xe2x80x9ca variator lensxe2x80x9d) 102 for zooming. The variator lens 102 shares the same optical axis with the first lens group 101. To vary its power, the variator lens 102 is moved in a direction in parallel with the optical axis of its own by driving means (not shown).
An iris 103 is disposed behind the variator lens 102 to adjust light quantity. Disposed further behind the iris 103 is a third lens group 104 that is attached onto the lens casing. The third lens group 104 also shares the same optical axis with the variator lens 102.
Arranged behind the third lens group 104 is a fourth lens group (hereinafter referred to as xe2x80x9ca focus-compensation lensxe2x80x9d) 105. The focus-compensation lens 105 has a focusing function, and a compensation function, namely compensating for the displacement of the focal plane arising from zooming. The focus-compensation lens 105 shares the same optical axis with the third lens group 104. The focus-compensation lens 105 is moved in a direction in parallel with the optical axis of its own by the driving means so that the focusing and compensation are performed.
An image pickup device 106 such as a CCD is arranged behind the zoom lens unit 100, namely the focus-compensation lens 105. An imaging surface that bears an optical image of an object is provided on one side of the CCD 106 facing the focus-compensation lens 105.
A wide-angle attachment lens 121 is mounted onto the zoom lens unit 100 in a detachable manner to modify the focal length and power of the lens unit 100. When mounted onto the zoom lens unit 100, the wide-angle attachment lens 121 is positioned in front of the first lens group 101 in a manner that allows the optical axes of both are aligned. The mounting of the wide-angle attachment lens 121 causes the focal length of the zoom lens unit 100 to shift toward the wide-angle side.
Discussed below referring to drawings are a relationship between the focal length (the position of the variator lens 102) of the zoom lens unit 100 and the position of the focus-compensation lens 105 with no wide-angle attachment lens 121 mounted and a similar relationship but with the wide-angle attachment lens 121 mounted. FIGS. 2(a) and 2(b) illustrate, respectively, the relationship between the focal length (the position of the variator lens 102) of the zoom lens unit 100 and the position of the focus-compensation lens 105 with no wide-angle attachment lens 121 mounted and the same relationship but with the wide-angle attachment lens 121 mounted in FIG. 1. FIG. 3 shows the relationship between the position of the variator lens and the position of the focus-compensation lens with no wide-angle attachment lens mounted in FIG. 1. FIG. 4 shows a similar relationship.
A discussion of the relationship between the focal length (the position of the variator lens 102) of the zoom lens unit 100 and the position of the focus-compensation lens 105 with no wide-angle attachment lens mounted follows.
When the focal length of the zoom lens unit 100 is set to a predetermined value, the position of the focus-compensation lens 105 that results in an optical image on the imaging surface of the CCD 106, namely, the focused position of the focus-compensation lens 105 varies with the distance to the object as shown in FIG. 2(a). When the object distance remains constant, the focused position of the focus-compensation lens 105 varies with the focal length of the zoom lens unit 100, namely, the position of the variator lens 102. As a result, an optical image is obtained through the light which is focused by shifting the focus-compensation lens 105 according to the curve resulting from the focal length set and the object distance.
A discussion of how to follow the above-mentioned curve follows.
Referring to FIG. 3, the relationship between the focal length (the position of the variator lens 102) of the zoom lens unit 100 and the position of the focus-compensation lens 105 with no wide-angle attachment lens 121 mounted is illustrated by a first curve f1 that is a plot of a series of positions of the variator lens 102, z0, z1, z2, . . . , z6 versus a corresponding series of positions of the focus-compensation lens 105, a0, a1, a2, . . . , a6. Data, z0, z1, z2, . . . , z6 and a0, a1, a2, . . . , a6, are stored in a lens control microcomputer (not shown). Equally, a second curve f2 is a plot of a series of positions of the variator lens 102, z0, z1, z2, . . . ) z6 versus a corresponding series of positions of the focus-compensation lens 105, b0, b1, b2, . . . , b6. These data are also stored in the lens control microcomputer.
A third curve f3, however, is calculated from the first curve f1 and the second curve f2. The third curve f3 is a plot of a series of positions of the variator lens 102, z0, z1, z2, . . . , z6 versus a corresponding series of positions of the focus-compensation lens 105, p0, p1, p2, . . . , p6. These data are also stored in the lens control microcomputer.
p0, p1, p2, . . . , p6 are calculated by the following equation.
p(n+1)={|p(n)xe2x88x92(n)|/|b(n)xe2x88x92a(n)|}*{|b(n+1)xe2x88x92a(n+1)|}+a(n+1)xe2x80x83xe2x80x83(1)
Equation (1) determines the ratio of interior division of p0 on a line segment, b0-a0, when the focus-compensation lens 105 is positioned at p0. According to the ratio, p1 is plotted on a line segment, b1-a1. The speed of the focus-compensation lens 105 required to keep the zoom lens unit 100 focused is thus determined by the positional difference between p1 and p0 and the time the variator lens 102 requires to travel from z0 to z1.
Referring to FIG. 4, interpolation applied to the variator lens 102 in its one direction is discussed. In FIG. 4, the position of the variator lens 102 is arbitrarily set, and representative (cam) locus (the positions of the focus-compensation lens relative to the variator lens) is a plot of the positions of the variator lens 102, z0, z1, z2, . . . , zn and a0, a1, a2, . . . , an, and b0, b1, b2, . . . , bn relative to the object distance.
When the variator lens 102 is positioned at zx, not on any of the zooming boundaries represented by z0, z1, z2, . . . , zn within the range of travel of the variator lens 102 (namely, somewhere between zk-1 and zk) and when the focus-compensation lens 105 is positioned at px, both ax and bx are given by the following equations.
ax=akxe2x88x92(zkxe2x88x92zx)*(akxe2x88x92akxe2x88x921)/(zkxe2x88x92zkxe2x88x921)xe2x80x83xe2x80x83(2)
bx=bkxe2x88x92(zkxe2x88x92zx)*(bkxe2x88x92bkxe2x88x921)/(zkxe2x88x92zkxe2x88x921)xe2x80x83xe2x80x83(3)
As understood from the above equations, ax and bx are determined by interpolating, respectively, between two sets of stored representative locus data (ak, and akxe2x88x921, and bk, and bkxe2x88x921 in FIG. 4) with respect to a fixed object distance according to the interior division ratios obtained from two sets of zooming boundaries (for example, zk and zkxe2x88x921 in FIG. 4) and the position of the variator lens 102 between zk and zkxe2x88x921.
As understood from Equation (1), both pk and pkxe2x88x921 are determined by interpolating, respectively, two sets of stored representative locus data (ak, akxe2x88x921, bk, and bkxe2x88x921 in FIG. 4) with respect to a fixed focal length according to the interior division ratio obtained from ax, px, and bx.
The travel speed of the focus-compensation lens 105 required to keep the zoom lens unit 100 focused is determined by the position difference between a focused position to be followed and the currently focused position in the zooming operation from a wide-angle side to a telephoto side and the time the variator lens 102 requires to travel from zx to zk.
The zoom lens unit 100 thus follows the curve representing the relationship between the focal length (the position of the variator lens 102) of the zoom lens unit 100 and the position of the focus-compensation lens 105 with no wide-angle attachment lens 121 mounted.
The relationship between the focal length (the position of the variator lens 102) of the zoom lens unit 100 and the position of the focus-compensation lens 105 with the wide-angle attachment lens 121 mounted is now discussed.
When the focal length of the zoom lens unit 100 is set to a predetermined value, the focused position of the focus-compensation lens 105 varies with the object distance as shown in FIG. 2(b). With the object distance kept constant, the focused position of the focus-compensation lens 105 varies with the focal length, namely with the position of the variator lens 102 (along a locus). As can be seen from FIG. 2(b), however, the curve representing the relationship, in terms of object distance as parameter, between the focal length and the position of the focus-compensation lens 105 is different from the curve representing the relationship, in terms of object distance as parameter, between the focal length and the position of the focus-compensation lens 105 with no wide-angle attachment lens 121 mounted. In FIG. 2(b), if the focal length exceeds a limit 301, the curves representing the relationship, in terms of object distance as parameter, between the focal length and the position of the focus-compensation lens 105 diverge out of the focusable focal length area. If the focal length is kept to within the limit 301, namely, the focal length is set to any value closer to the wide-angle side, focus adjustment by means of the focus-compensation lens 105 remains workable. If the focal length exceeds the limit 301, however, namely, the focal length is set to any value closer to the telephoto side, focus adjustment by means of the focus-compensation lens 105 is impossible. To cope with this problem, the variator lens 102 is moved until the focal length is set to be closer to the wide-angle side, and is fixed there.
Therefore, the variator lens 102 is fixed at such a predetermined position, and zooming operation is disabled when the wide-angle attachment lens 121 is mounted.
When the zooming operation is disabled with the wide-angle attachment lens 121 mounted, however, the magnification of the zoom lens unit 100 with the wide-angle attachment lens 121 mounted is fixed. A fine adjustment of field of view by modifying slightly the magnification of the zoom lens unit 100 with the wide-angle attachment lens 121 mounted is not possible, and a user cannot compose a picture as intended.
For example, assuming that the magnification of the zoom lens unit 100 is set to a range from 1xc3x97 to 12xc3x97, and the magnification of the zoom lens unit 100 with the wide-angle attachment lens 121 mounted is set to a range from 0.7xc3x97 to 1xc3x97, the disabling of the zooming operation at the mounting of the wide-angle attachment lens 121 sets the magnification to 0.7xc3x97. Although by detaching the wide-angle attachment lens 121, the setting of 1xc3x97 to 12xc3x97 is recovered, any magnification setting between 0.7xc3x97 and 1xc3x97 cannot be made.
When the zooming operation is enabled with the wide-angle attachment lens 121 mounted, focus adjustment is possible within a certain range of focal length; however, if the variator lens is moved within the focusable focal length area, focus adjustment cannot follow the shift of the variator lens 102, and thus focused state cannot be properly maintained.
It is a first object of the present invention to provide a lens control device and a camera, which perform a zooming operation while keeping a focused state and allow a user to set a field of view as intended, when a wide-angle attachment lens is mounted.
It is a second object of the present invention to provide a camera which causes no unfocused state when a wide-angle attachment lens is mounted.
It is a third object of the present invention to provide a camera which allows zooming operation when a wide-angle attachment lens is mounted.
To achieve the above objects, a preferred embodiment of the present invention comprises a variator lens group for zooming, a focusing lens group for compensating for a change introduced into the focused position as a result of a zooming operation by the variator lens group, a conversion lens group for changing a focusable shifting area of the variator lens group from a first area to a second area, computing means for determining driving information used to drive the focusing lens group during the shifting of the variator lens group, based on focused position data, according to object distance, of the focusing lens group relative to the position of the variator lens group, position data of the variator lens group and position data of the focusing lens group, and control means for shifting the variator lens group from the first area to the second area in response to the mounting of the conversion lens group and for controlling a computing operation of the computing means so that a focused position of the focusing lens group is determined when the variator lens group moves within the second area.
The present invention in another preferred embodiment provides a lens control device, wherein data of the focused position, set according to object distance, of the focusing lens group with respect to the variator lens group are made up of first focused position data regarding the first area and second focused position data regarding the second area.
The present invention in yet another preferred embodiment provides a lens control device, wherein data of the focused position, set according to object distance, of the focusing lens group with respect to the variator lens group are made up of first focused position data regarding the first area and the computing means determines second focused position data regarding the second area based on the first focused position data.
The present invention in yet another preferred embodiment provides a lens control device, wherein the computing means selects either the first focused position data or the second focused position data in response to the mounting or demounting of the conversion lens group, and computes the focused position data of the focusing lens group during the shifting of the variator lens group based on the selected first or second focused position data.
In the above preferred embodiments, the computing means thus computes the focused position data of the focusing lens group during the shifting of the variator lens group, when the variator lens group is shifted within the second area with the conversion lens group mounted.
It is a fourth object of the present invention to provide a camera which permits smooth zooming operation by optimizing the driving speed of the variator lens according to the range of travel of the variator lens that is shifted in response to the mounting of the conversion lens such as a wide-angle attachment lens.
It is a fifth object of the present invention to provide a camera which permits smooth and easy-to-use operation by allowing an operator to recognize the range of travel of the variator lens, namely, the focusable focal length area of the variator lens which is shifted in response to the mounting of the conversion lens such as the wide-angle attachment lens.
It is a sixth object of the present invention to provide a camera which reactivates AF (Automatic Focusing) operation in response to the mounting of the conversion lens to prevent unfocused state which is attributed to a change in the optical characteristics of the lens with the conversion lens such as the wide-angle attachment lens mounted.
These and other objects and features of the present invention will be more apparent when the following detailed description is considered with the attached drawings.